Stopped awaiting the connected event in ports isolator tests.
Stopped awaiting the connected event in ports isolator tests.

Rather than explicitly waiting for the `connected` scheduler event,
consistently apply the testing pattern from the default executor
tests. We expect that the `connected` event happens, but we only
need to synchronize the test on the `subscribed` event.

Review: https://reviews.apache.org/r/63183/

gsantovena/mesos,jpeach/mesos,jpeach/mesos,kaysoky/mesos,reneploetz/mesos,kaysoky/mesos,Gilbert88/mesos,asamerh4/mesos,Gilbert88/mesos,andschwa/mesos,Gilbert88/mesos,gsantovena/mesos,chhsia0/mesos,reneploetz/mesos,asamerh4/mesos,asamerh4/mesos,asamerh4/mesos,andschwa/mesos,andschwa/mesos,dforsyth/mesos,dforsyth/mesos,kaysoky/mesos,chhsia0/mesos,dforsyth/mesos,kaysoky/mesos,dforsyth/mesos,abudnik/mesos,reneploetz/mesos,Gilbert88/mesos,andschwa/mesos,abudnik/mesos,reneploetz/mesos,chhsia0/mesos,kaysoky/mesos,asamerh4/mesos,reneploetz/mesos,dforsyth/mesos,abudnik/mesos,gsantovena/mesos,abudnik/mesos,jpeach/mesos,gsantovena/mesos,jpeach/mesos,Gilbert88/mesos,chhsia0/mesos,kaysoky/mesos,abudnik/mesos,reneploetz/mesos,andschwa/mesos,asamerh4/mesos,andschwa/mesos,chhsia0/mesos,chhsia0/mesos,reneploetz/mesos,dforsyth/mesos,gsantovena/mesos,andschwa/mesos,abudnik/mesos,chhsia0/mesos,gsantovena/mesos,jpeach/mesos,jpeach/mesos,gsantovena/mesos,Gilbert88/mesos,jpeach/mesos,asamerh4/mesos,Gilbert88/mesos,kaysoky/mesos,dforsyth/mesos,abudnik/mesos